A very common type of seat belt system used in passenger cars and other automotive vehicles includes a shoulder belt that leads from an anchor affixed to the center pillar of the vehicle body at a location outboard of, above and behind the shoulder of the occupant of the seat inwardly and downwardly across the torso of the occupant to a buckle or other fastening device located adjacent the lower rear of the inboard side of the seat. Such a shoulder belt may be used in conjunction with a lap belt or with an energy absorbing knee bolster. It has been proposed in the past that the belt anchor on the center pillar be mounted for adjustment of its position in the vertical direction so that the shoulder belt will fit better to the physique of the particular occupant.
FIG. 1 of the accompanying drawings illustrates a known adjustable belt anchor of the type used on the center pillar for the upper outboard end of a shoulder belt. The center pillar has a slot 1 that opens into the passenger compartment. A reinforcing plate 3 having a multiplicity of vertically spaced-apart notches 2 is installed within the center pillar adjacent the slot. A locking plate having a pair of vertically spaced-apart forwardly projecting flanges 4 is received behind the reinforcing plate 3 with the flanges received in a selected adjacent pair of the notches 2. The shoulder belt 6 is received by an anchor plate 7 that, in turn, is connected to the reinforcing plate by a bolt 8 that extends through the locking plate into a nut 10. A saucer-shaped spring 9 is received between the head of the bolt 8 and the anchor plate 7 and allows the anchor to be repositioned along the reinforcing plate 3 by pushing in on the head of the bolt, thereby deforming the spring 9, pushing rearwardly on the nut and locking plate and disengaging the flanges 4 from the notches 2. The anchor assembly can then be adjusted up or down, and upon release of pressure on the bolt head, the spring 9 pulls the nut 10 and the locking plate 5 forwardly to position the flanges 4 in another pair of notches 2. This anchoring arrangement is somewhat unstable because of the presense of the spring 9, and inward components of force on the belt 6 can easily overcome the spring force and produce rocking and cocking motion of the assembly relative to the desired stable position in engagement with the reinforcing plate.